1. Field of the Invention
The invention relates to a sanitary tub with an outer shell made of a steel sheet, an inner shell made of plastic, and an intermediate layer connecting the two shells. A protective coating is applied to the outer shell for protection against corrosion.
2. The Prior Art
Sanitary tubs are known from DE-C 44 31 716, in which the outer shell is pickled and basically enameled on the back side. Since the adhesion of the intermediate layer consisting of a polyurethane or a methacrylic compound is inadequate on an enameled surface, no enameling is provided on the inner surface of the steel sheet shell. This makes manufacturing of the tub more difficult because a commonly used immersion process cannot be applied for the enamel coating. The coating of enamel applied to the inner side has to be mechanically removed, for example by sandblasting, or at least have the surface roughened. According to another design described in DE-C 44 31 716, the outer shell, which is deep-drawn from steel sheet, is pickled and passivated before the acrylic shell is molded on the inner side and glued to the steel blank. In a last process step, the rust-preventing coating is applied to the outer shell of the composite tub. In this step, the ledge and the inner side of the composite tub, which is already manufactured, have to be covered by a costly process. Furthermore, there is the risk that the protection against corrosion may be incomplete along the ledge of the tub because of the required coverings.